A photonic crystal has a photonic band gap formed by a periodical arrangement of different dielectric constants. The photonic crystal may be applied to lasers, optical switches or the like. Two-dimensional photonic crystal structures may be classified into a triangular lattice structure and a square lattice structure according to lattice structure.
When a resonator is designed in a photonic crystal, a single-cell resonator may be provided by introducing a single crystal. In addition, a linear type resonator may be provided by introducing linearly arranged crystals or a ring type resonator may be provided by introducing ring type crystals. A photonic crystal resonator may generate a laser by introducing a gain medium into a resonator.